Optical disk employing integral substrate, and method for manufacturing the same

ABSTRACT

An optical disk, which comprises: a common integral substrate having grooves and/or pits formed on its both sides: and a film structure on at least one side of the integral substrate. They are manufactured by preparing two stampers; simultaneously forming grooves and pits on both sides of an integral substrate by use of said two stampers mounted on a respective fixed mold and moving mold; and forming the film structure on at least one side of said integral substrate by depositing material from targets suspended to both sides of said integral substrate. The disks are superior in mechanical properties and reliability. As for reliability, the present optical disk is prepared without using a bonding process, which overcomes the problem of adhesive out-flow. The presence of only one integral substrate brings about an increased data storage density, twice as much per substrate, while contributing to the lightness of disk and accompanied by various effects including reduction in access time, saving of the bonding process and time in the spin coating, and cost reduction.

This application is a Divisional Application of U.S. application Ser.No. 09/690,830, filed Oct. 18, 2000 now U.S. Pat. No. 6,623,828; whichis a Continuation-in-Part Application of U.S. application Ser. No.08/591,978, filed Jan. 29, 1996 now U.S. Pat. No. 6,150,000; and whichclaims priority under 35 U.S.C. §§ 119 and/or 365 to 95-1802, filed inKorea on Jan. 28, 1995; the entire content of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a novel optical disk and,more particularly, to the use of an integral substrate to form anoptical disk, which has pits and/or grooves formed on the oppositesurfaces, without junction parts, thereby obtaining an improvement inreliability and mechanical properties of the resulting substrate at areduced cost. Also, the present invention is concerned with a method formanufacturing the optical disk.

2. Description of the Prior Art

As society becomes more and more information-intensive, it produces anenormous quantity of various information every day. Thus, recordingmedia with higher data storage density, higher data transfer rate andlonger data archival capability are necessary to cope with thisinformation explosion. Further, recording media are required to be ofhigh recording sensitivity with consideration of the margin betweendrives of different electromagnetic machines. In response to theseneeds, optical recording media were created and, since their creation,have been continuously developed.

Among the optical recording media are a magneto-optical disk(hereinafter referred to as “MOD”), a super density disk (hereinafterreferred to as “SD”), a Random Access Memory (hereinafter referred to as“RAM”), a Digital Versatile Disc (hereinafter referred to as “DVD”), aMini Disc (hereinafter referred to as “MD”), a Digital VersatileDisc-Rerecordable (hereinafter referred to as “DVD-RW”), a DigitalVersatile Disc Rewritable (hereinafter referred to as “DVD+RW”) and aDigital Versatile Disc-Recordable (hereinafter referred to as “DVD-R”).MOD is capable of recording and reading data by forming a magneticlayer, on a substrate, whereas SD is incapable of rewriting theinformation stored because they are formed with a stamper during amastering process, and when making stamper, data is recorded in pitswithout a recording layer.

SD's have recently come into the spotlight in recording media marketsnot only because they have 10 to 600 times higher recording density as amagnetic recording medium, but also because information can be storedsemi-permanently in them by virtue of non-contactingrecording/reproducing manner between a head and the medium.

In order to better understand the background of the invention, adescription of conventional MOD and SD will be given below, inconnection with some drawings.

Referring to FIG. 5, there is depicted a conventional MOD ofdouble-sided structure that is prepared by bonding two identicalsubunits to each other using a hot melt bonding layer 50. Each subunithas a polycarbonate substrate 20 a and 20 b, one side of which iscovered with a hard coating protective film 60 a and 60 b and the otherside of which has a tetralayer arrangement. The tetralayer arrangementincludes a first dielectric film 21 and 25, a magnetic recording film 22and 26, a second dielectric film 23 and 27, and a reflective film 24 and28 protected by a seal coating film 29 is formed.

With reference to FIG. 7, there is depicted a structure of aconventional SD. Like the conventional MOD, the SD has two identicalsubunits, each having a substrate 71 and 77 on which a semi-transparentfilm 72 and a reflective film 76 and a seal coating film 73 and 75 aresequentially formed. These subunits are symmetrically arranged with anUV bonding layer 74 interposed therebetween.

Referring to FIG. 3, there is shown a conventional manufacturing processfor a substrate of a MOD. As shown in this figure, a substrate 2 ismanufactured through injection molding. In this process, only a stamper3 is mounted on a fixed mold 4 and forms pits and grooves on one side ofthe substrate 2, which is in direct contact with a movable mold 1. Withthis polycarbonate substrate, the tetralayer arrangement and theprotective layer are formed for MOD and the bilayer arrangement for SD.

The substrate of the conventional MOD or SD should undergo film-formingprocesses for the tetra- or bilayer arrangement, a spin coating processfor the protective film and the bonding process for junction of twosubunits. In the course of these processes, there is a strongpossibility that the mechanical properties of the substrates may bedegraded. This is highly apt to cause a problem in rotating the disk ata high rate which relates to data transfer rate.

The bonding of the two subunit disks can be usually achieved through useof a hot melt adhesive or UV setting resin. When a hot melt adhesive isused, a protective film made of hard coating resin, which plays a rolein preventing flaws on the recording side of the polycarbonatesubstrate, is formed. In this case, the hot melt adhesive on theprotective film may flow out and stick to the cartridge, giving rise toa serious problem in reliability. In the latter case, the UV settingresin is coated and exposed to be cured, which saves time. However,there occurs a problem in that, since the UV setting resin may flow outof the margin, it is required to be trimmed.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above problemsencountered in prior art and to provide an integral substrate theopposite sides of which are molded through an injection molding process,thereby saving the adhesive process using a hot melt adhesive or UVsetting resin.

It is another object of the present invention to provide an optical diskwhich employs the integral substrate.

It is a further object of the present invention to provide a method formanufacturing the optical disk, using the integral substrate.

Intensive research repeated by the present inventors aiming to developan optical disk, which is significantly improved in reliability andproduction cost, has resulted in finding that one integral substrate, onboth sides of which grooves and/or pits can be formed, is sufficient todesign an optical disk structure.

In accordance with an aspect of the present invention, there is providedan integral substrate for an optical disk, possibly having groovesand/or pits on both of its sides, without junction parts at its center.

In accordance with another aspect of the present invention, there isprovided an optical disk, comprising an integral substrate possiblyhaving grooves and/or pits formed on both sides, and a stack structure,comprising a reflective film, a first dielectric film, an opticalrecording film, a second dielectric film and a protective layer whichare, in sequence, laminated on at least one side of said integralsubstrate.

In accordance with still a further aspect of the present invention,there is provided a method for manufacturing an optical disk, comprisingthe steps of: preparing two stampers; forming grooves and/or pits on oneor simultaneously on both sides of an integral substrate, by use of saidtwo stampers mounted on a fixing mold and a moving mold, respectively;and forming a film structure on at least one side of said integralsubstrate, by depositing targets suspended on at least one side of saidintegral substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing a clockwise recording manner oflaser beam recorder upon mastering process;

FIG. 2 is a schematic diagram showing a counterclockwise recordingmanner of laser beam recorder upon mastering process, according to thepresent invention;

FIG. 3 is a schematic cross sectional view showing a conventionalsubstrate for magneto-optical disk prepared by an injection moldingprocess;

FIG. 4 is a schematic cross sectional view showing a substrate for anoptical disk prepared by an injection molding process, according to thepresent invention;

FIG. 5 is a schematic diagram showing the structure of a conventionalmagneto-optical disk;

FIG. 6 is a schematic diagram showing the structure of an optical diskaccording to the present invention;

FIG. 7 is a schematic diagram showing the structure of a conventionalSD; and

FIG. 8 is a schematic diagram showing the structure of a SD among anoptical disk according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention are best understoodwith reference to the accompanying drawing.

With reference to FIG. 4, there is shown a manufacturing process for asubstrate, according to the present invention. As shown in this figure,a substrate 12 is manufactured by injecting polycarbonate resin betweentwo stampers 13 a and 13 b which are mounted on two molds, a fixed mold14 and moving mold 14. Stamper 13 b mounted on moving mold 11 may be adummy i.e., bearing no information content. A substrate havinginformation on one side can be prepared by using such a dummy stamper.Even though stamper 13 b is dummy, two stampers 13 a and 13 b aremounted on two molds and thus it can make the surface materials andconditions the same. This makes the flow of resin smooth upon injectionmolding to improve the roughness of both or one of substrates. As aresult, it decreases a noise during recording and reproducing of theinformation.

Referring to FIG. 6, there is an optical disk having a common substrate30 on the opposite sides of which tetralayer structures coated with aseal coating 39 a and 39 b is formed. Each of the tetralayer structurescomprises a reflective film 34 and 38, a first dielectric film 33 and37, a recording film 32 and 36 and a second dielectric film 31 and 35.These films are sequentially laminated on each side of the substrate.Accordingly, the optical disk of the present invention, unlike theconventional optical disk, is structured to have a common integralsubstrate which has a reflective film, a first dielectric film, arecording film, a second dielectric film and a protective layersequentially formed on at least one side thereof. The thickness of thesefilms is not confined and may be varied properly according to what is tobe achieved.

The substrate is characterized in that it may have pits and/or groovesformed on both sides. The pits and grooves are not limited in length andmay be formed by otherwise conventional processes. Various materials,for example, polycarbonate, APO(Amorphous Poly Olefin), PMMA(Polymethylmetacrylrate) and glass were used for substrate and polycarbonate ispreferred due to its low price.

Information is recorded in the recording layer 32 and 36 which consistsmainly of TbFeCo, TbFeCoCr, NdTbFeCo, NdFeCo, NdDyFeCo, GeSbTe,AgInSbTe, or GeAgInSbTe. Examples of the dielectric films 31, 33, 35 and37 include SiN, SiO2, ZrO2, and ZnS—SiO2 with a preference of SiN. Forthe reflective films 34 and 38, Al, Al—Ti, Cu, Ag, Au or AgInPd is used,with a preference for Al. For the protective layer 39 a and 39 b, aresin such as polyacrylate, polycarbonate, APO(Amorphous Poly Olefin),PMMA(Polymethyl metacrylrate) and glass were used and polyacrylate ispreferred.

FIG. 8 shows a structure of an SD according to the present invention.Like the magneto-optical disk of the present invention, the SD has acommon integral substrate 83. On one side of the integral substrate 83 asemi-transparent film 82 and a seal coating protective film 81 issequentially formed, and on the other side of which a reflective film 84and a seal coating protective film 85 is sequentially formed. In thisembodiment, information is recorded in the pits and grooves formed onboth sides of the integral substrate 83. The semi-transparent film 82 ismade of a material having a reflective rate of about 30 to 40, examplesof which include SiN, SiO2, ZrO2 and Au with a preference for SiN. Forthe reflective film 84, a material with a reflective rate of 85% or moreis employed, including Al and Al—Ti. Al is preferred. As in an opticaldisk, the thickness of these films is not confined.

Following are of processes for manufacturing the optical disk inaccordance with the present invention. The processes will be describedin detail in connection with the drawings.

A photoresist film on a master glass is exposed, as shown in FIG. 2,counterclockwise to a laser beam, to form the stamper. Thiscounterclockwise direction is opposite to the conventional recordingmanner of laser beam recorder (hereinafter referred to as “LBR”). Thatis, during the mastering process for the conventional MOD, the recordingmanner of LBR is carried out in a clockwise direction, as shown in FIG.1. Conventional MODs, consisting of two identical subunits bonded witheach other, are usually designed in such a way that a laser beam forrecording or reproducing information may be incident from the sidesurfaces of the substrates. In contrast with conventional MODs, theoptical disk according to the present invention is designed in such away that information may be recorded or reproduced by incidence of alaser beam upon the groove face of the polycarbonate. This difference isowing, as delineated above, to the fact that the structure of theoptical disk of the present invention is almost a reverse to that of theconventional MOD. Accordingly, the counterclockwise direction for thestamper is intended to make the optical disk of the present inventionapplicable to existing drives.

As shown in FIG. 4, two stampers 13 a and 13 b are respectively mountedto the fixed mold 14 and the moving mold 11. Thereafter, polycarbonateresin, APO(Amorphous Polyolefin), PMMA(Polymethylmetacrylrate) or glassis injected between the two stampers which are facing on each other, toform substrate 30 with desirable grooves and/or pits on its both sides.Two identical targets of a kind can be suspended to the two oppositesides of the chamber of a sputter M/C, each target in order to equallyand simultaneously deposit material on both sides of the monolayersubstrate 30. The substrate can be made in various molding processes,for example, compression molding, injection molding or compressiveinjection molding, according to the purpose of the resulting opticaldisk, and preferably in injection molding process. These film-formingprocesses may be carried out under various conditions according to thepurpose of the resulting optical disk. Also, the thickness andcomponents of the films to be formed may be properly changed dependingon the purpose.

In the present invention, as shown in FIG. 6, an aluminum reflectivefilm 34 and 38, a first dielectric film 33 and 37, an optical recordingfilm 32 and 36 and a second dielectric film 31 and 35 are, in sequence,deposited on each side of substrate 30, followed by the deposition of aprotective layer 39 a and 39 b, for example.

For SD, as shown in FIG. 8, a semi-transparent film 82 and a sealcoating protective film are sequentially laminated on the integralsubstrate 83 beneath which a reflective film 84 and a seal coatingprotective film 85 are formed.

Accordingly, the present invention is an optical disk with an integralsubstrate which is capable of having the same data storage capacity asthat of a conventional MOD with two polycarbonate substrates. That is,the optical disk according to the present invention can be of twice datastorage density per substrate. The substrate of the conventional MOD islikely to be bent during the film-forming processes because the stressresulting from the stacking of the films exerts only on one side of it.In contrast with the conventional substrate, the substrate of thepresent invention can have the films formed identically on its bothsides and thus exert an identical quantity of the stress on the bothsides such that the substrate is almost free of bending. Besides, asingle substrate enables the present optical disk to be reduced in tacttime into one third of that of the conventional MOD having twosubstrates and as well as to have twice data storage density persubstrate, thereby improving productivity.

A better understanding of the present optical disk may be obtained inlight of following examples which are set forth to illustrate, but arenot to be construed to limit, the present invention.

EXAMPLE I

Photoresist on a master glass was recorded in a counterclockwisedirection by a laser beam, to prepare a stamper. Two such stampers 13 aand 13 b were mounted to a fixed mold 14 and a moving mold 11 each, asshown in FIG. 4. Thereafter, polycarbonate resin was injected into aspace between the two stampers, to form grooves and pits to both sidesof the substrate. Targets were suspended on opposite sides of thechamber of a sputter M/C, to form a 400 Angstrom Al reflective film, a200 Angstrom SiN dielectric film, a 200 Angstrom magnetic recording filmand a 600 Angstrom SiN dielectric film on each side of the substrate 30,each side undergoing simultaneous operations. These film-formingprocesses were carried out under a pressure of about 10 mbar and at apower of about 2 kW. Thereafter, seal coating resin was spin-coated onthe two outermost aluminum reflective surfaces, to form protective filmsless than 150 μm thick each.

EXAMPLE II

A SD was prepared as follows. As in Example I, stampers, each of whichwas different in information content, were prepared. Two stampers 13 aand 13 b, as shown in FIG. 4, were mounted to the fixed mold 14 andmoving mold 11, respectively, in order to form information pits on bothsides of the polycarbonate substrate. Targets were suspended on bothsides of the chamber of a sputter M/C with a pressure of 10 mbar and apower of about 2 kW, to form a 500 Angstrom SiN semi-transparent film 82and a 500 Angstrom Al reflective film 84 on the opposite sides of thesubstrate, respectively, after which the seal coating resin wasspin-coated to form a protective film 8-10 μm thick on thesemi-transparent film and the reflective film.

COMPARATIVE EXAMPLE I

A stamper was mounted only to a fixed mold, as shown in FIG. 3. Usingthe mold, polycarbonate resin was subjected to injection molding, togive a substrate with grooves and pits formed on its one side. On thisside, a 600 Angstrom thick SiN dielectric film, a 200 Angstrom thickmagneto-optical recording film, a 200 Angstrom thick SiN dielectric filmand a 400 Angstrom thick aluminum reflective film were formed, insequence, using a dielectric current magnetron sputtering process. Twodisks thus obtained were bonded with each other, in such a way that theoutermost reflective film in one disk faces on its counterpart with ahot melt adhesive interposed therebetween. Finally, a hard coating resinwas spin-coated on the entrance surfaces of the substrates, to form twoouter hard coatings with a thickness of 3 μm. The optical disk preparedin Example I and Comparative Example I were tested for mechanicalproperties using a measuring apparatus commercially available from OnoSokki Co. Ltd., Japan, identified as model No. LM-100A. While rotatingthe disks in a speed of 2,400 rpm, mechanical properties were measuredat locations apart from the center by 30, 40, 50 and 60 mm by use of areproducing power of 0.7 mW.

Averages of the measurements are given as shown in Table 1 below.

TABLE 1 Mechanical Properties of Optical Disk Axial deflect Axial AccTilt Radial Acc Example No. μm m/sec² mrad m/sec² Com. Exam. I  70-100 8-14 2-3 2-3 Exam. I 20-30 4-6 1 2-3 Exam. II 20-30 6-8 2 2-3

The optical disk prepared in Example I and Comparative Example I weremounted on respective drivers and tested for reliability in an incubatorin which its temperature was maintained at 80° C. under a relativehumidity of 85%. The results are given as shown in the following Table2.

TABLE 2 Attachment State in Disk upon Incubation Test Time Example No.Initial 1 day 5 days 10 days 20 days 30 days Com. Exam. I 0 0 0 X — —Exam. I 0 0 0 0 0 0 Exam. II 0 0 0 0 0 0

In this test, the hot melt adhesive flowed out the MOD obtained inComparative Example I within 10 days and stuck to the cartridge.

As apparent from the examples and tables, the optical disk of thepresent invention is superior to conventional ones in mechanicalproperties and reliability. As for reliability, the present optical diskis prepared without using a bonding process, which completely overcomesthe problem of out-flowing of adhesive. The common single substrateresults in twice the data storage density per substrate and capacitatesthe optical disk to improve in birefringence because of directpenetration of laser beam, not through substrate, into the recordingfilm. In addition, since the substrate has multilayer films equally onits both sides, it is free of bending.

Further, the presence of only one substrate contributes to thelightening of the disk, which brings about accompanying effectsincluding, for example, reduction in access time, saving of the bondingprocess and time in the spin coating, and reducing cost.

The present invention has been described in an illustrative manner, andit is to be understood that the terminology used is intended to be inthe nature of description rather than of limitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, it is to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. A method for manufacturing an optical disk,comprising the steps of: preparing two stampers; forming grooves and/orpits on at least one side of an integral substrate by use of said twostampers mounted on respective molds, at least one of which is movablerelative to the other; and forming a film structure on at least one sideof said integral substrate by depositing targets suspended at said sideof said integral substrate, wherein said step of forming the filmstructure comprises the step of: providing a reflective film, a firstdielectric film, an optical recording film, a second dielectric film anda protective layer in sequence on at least one side of said integralsubstrate.
 2. The method in accordance with claim 1, wherein saidpreparing step comprises developing a photoresist counterclockwise on amaster glass by use of a laser beam.
 3. The method in accordance withclaim 1, wherein one of two stampers comprises a dummy stamper.
 4. Amethod for manufacturing an optical disk, comprising the steps of:preparing two stampers; forming grooves and/or pits on at least one sideof an integral substrate by use of said two stampers mounted onrespective molds, at least one of which is movable relative to theother; and forming a film structure on at least one side of saidintegral substrate by depositing targets suspended at said side of saidintegral substrate, wherein said step of forming the film structurecomprising the step of: providing a reflective film, a first dielectricfilm, an optical recording film, a second dielectric film and aprotective layer in sequence on both sides of said integral substrate.5. The method in accordance with claim 4, wherein said preparing stepcomprises developing a photoresist counterclockwise on a master glass byuse of a laser beam.